Electrical apparatus



CROSS REFERENCE S R I SUBSTITUTE FUR MISSING XR ELECTRICAL APPARATUS 2Sheets-Sheet 1 Filed Nov. 30, 1942 DIFFERENTIALLY HI 6 5 2555" 47 48 as.46 25 n F 17 g 26 3 3 a ll/ "41 J6 Q R38 I! i 7 E I 1 l I 50 41 l .5923 16 52 5 go 37 46 Z8 5'H- I FIG. 5

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16' 1.9 Q1? Low- Jr c o I Wm FREQUENCY c J r O RECORDER a {P AMPLIFIER-INVENTOR i7 DETECTOR T OYAL LEE w HIGH-FREQUENCYL/ZO V B) OSCILLATORMETER ATTORNEY REARGR mm;

Aug. 16, 1949.

R. LEE

ELECTR I CAL APPARATUS Filed NOV. 30, 1942 FIG. 8 46 2 Sheets-Sheet 2INVENTOR ROYAL LEE ATY'ORNEY Patented Aug. 16, 1949 UNITED STATES PATENTOFFICE 8 Claims.

microphone which is of simple and rugged construction and has a goodresponse to impressed vibrations.

A still further object is to provide electrical apparatus which is soarranged as to form a simple and reliable dimension gauge.

The invention further consists in the several features hereinafterdescribed and claimed.

In the accompanying drawings, illustrating certain embodiments of theinvention,

Fig. 1 is a side elevation of a translating device incorporatingfeatures of the invention and arranged to form a microphone;

Fig. 2 is a sectional elevation taken generally along the line 2-2 ofFig. 1;

Fig. 3 is a sectional elevation taken generally along the line 33 ofFig. 2;

Fig. 4 is a sectional view taken generally along the line 4--4 of Fig.3;

Fig. 5 is a detail sectional elevation taken generally along the line5-5 of Fig. 3;

Fig. 6 is a detail view of a casing band of the device;

Fig. 7 is a diagrammatic view of an electrical system for themicrophone;

Fig. 8 is an elevation of a modified form of microphone apparatusadapted for measuring or checking the surface finish of a work piece;

Fig. 9 is a front elevation of work-gauging apparatus arranged inaccordance with the invention and adapted for gauging an opening in awork piece;

Fig. 10 is an enlarged sectional elevation of part of the work-gaugingapparatus of Fig. 9;

Fig. 11 is a front elevation of a modified form of gauging apparatusadapted for gauging an external dimension of a work piece, and

Fig. 12 is a diagrammatic view of an electrical system for the gaugingapparatus of Figs. 9 and 11.

Referring to Figs. 1 to '7 of the drawings, a microphone or signaltranslating device is designated generally by the numeral 15. Themicrophone includes coils l6 and i1 arranged in proximity to each otherand relatively movable to vary the coupling between them. These coils,which form a variable inductor, are preferably connected in series andare arranged differentially or in opposing relation. The coils are ofthe spirally wound flat or pancake type arranged side by side in coaxialrelation and are preferabl identical and of small size, usuallyconsiderably less than one inch in diameter. The coil spacing is small,being usually less than 1 inch.

The microphone coils are mounted for relative vibratory movement ashereinafter described, and are connected in a suitable electrical systemsuch as that of Fig. 7. In this system, the variable inductor consistingof the two coils l6 and I! is connected across the input terminals of adetector or demodulator l8 and in some cases may be shunted by a smallvariable condenser IS. A high-frequency oscillator 20 of any suitabletype, such as an electron-coupled type, impresses a high-frequencyvoltage on the input terminals of the detector. In some instances theoscillator may be crystal-controlled. The oscillator frequency is notcritical and may be selected from a wide range of values such as from 30kilocycles per second to 500 kilocycles per second, although these arenot to be regarded as limiting values. In general, the use of the higherfrequencies is desirable as the microphone coils can then be made smalland light. The tuned parallel input circuit of the detector, comprisingthe connected microphone coils and their shunting capacities, is set toa frequency slightly above or below the oscillator frequency byadjusting the variable condenser [9 (or by adjusting the oscillator), sothat the normal operating point of the detector is not at the crest ofthe resonance curve but lies on one of the sloping sides of the curve.The relative movement of the microphone coils under impressed mechanicalvibrations changes the reactance of the detector input circuit, and thusproduces a I correspondingly modulated detector output. The

The relatively movable microphone coils l6 and H are mounted within ametal shielding casin comprising a cylindrical cup 25 closed at its endby a disk 26. A hook-shaped bracket 21 within the casing is rigidlysecured to the end wall of the cup by screws 28. Two parallel studs 29are riveted to the bracket and extend in the diametral plane of the cup25 and parallel to the axis of the cup. A flat plate 30 of insulatingmaterial extends at right angles to the cup axis and has apertured endportions slidably supported on the reduced threaded ends of the studs,the plate ends being confined between nuts 3| on the studs andcompressed coiled springs 32 surrounding the studs. The flat microphonecoil I6 is secured to the plate, as by a suitable adhesive, and issubstantially coaxial of the casing. By turning the nuts 3 I, the plateand attached coil can be axially adjusted in the casing.

Two spring arms 33, preferably in the form of leaf springs, are spacedfrom opposite sides of the coil-supporting plate 30 and extendsubstantially parallel to the plate. The leaf springs, which have theshape seen in Fig.5, are each secured at one end to the bracket 2! as byscrews 34, and each spring has its inner portions cut away to form areentrant tongue 35 attached to the free end of the spring, thusincreasin the effective length of the spring. A stem 35 of insulatingmaterial extends between the leaf springs along the axis of the casingand is rigidly secured at opposite ends to the aperture-d tongues 35 ofthe spaced springs, the stem extending through the apertured centralportion of the coil-supporting plate 30. The end of the stem adjacent tothe end wall of the cup 25 is fastened to the adjacent leaf spring by anut 31, and the other end of the stem is fastened to the correspondingleaf spring by a screw threaded shank 38 formed on a fiat damp ing disk39. The damping disk, which also forms on inertia member, fits looselywithin the cylindrical cup 25 out of contact therewith A microphonecable 42, preferably of the coaxial type, is suitably anchored on thebracket 21, as by a terminal-forming grommet 43, and has its terminalsconnected to the coils I6 and H, the cable extending through an opening44 in the casing cup 25. A pair of complementary cupshaped housingmembers 45 of insulating material snugly enclose the casing 25, 26 andhave registering notches 46 at their meeting edges to accommodate thecable. The cup-shaped housing members have enlarged rim portions 41which are retained in assembled relation by a surrounding resilientmetal band 48 with inturned marginal flanges 49. The ends of the bandare provided with complementary halves of a screw-threaded sleeve 50through which the cable passes, and the split band is held in clampedposition by a collar nut 5| surrounding the sleeve. The ends of thehousing members are crowned and a loop member 52 is secured to one ofthese ends to receive a strap or tape, not shown, by which themicrophone may be secured to a. vibration-transmitting surface. When themicrophone is used for diagnostic work, in the manner of a stethoscope,the crowned end of the housing is placed against the body of a patientand the device is usually strapped or taped in position.

In operation, the vibrations of the source are transmitted to thecontacting housing of the microphone, causing the housing and the partsof the device rigid therewith, including the coil IE, to vibrate inunison. The coil I'I, however, which is supported by the leaf springs33, tends to remain stationary because of the inertia of the dampingdisk 33 and other parts rigid with the coil I7, and the result is arelative vibration of the two coils in accordance with the impressedvibrations. The inductance of the associated coils'IB and I1 variesaccordingly, decreasing as the coils move toward each other andincreasing as they move apart. The varyin inductance changes thereactance of the detector input circuit which is connected to theconstant frequency oscillator 29, thus producing a modulated detectoroutput. The resulting signal is then amplified and applied to one ormore of the output devices 22, 23 and 24.

By connecting the microphone coils in series opposing relation, arelatively large change in inductance is effected for a comparativelysmall change in the coil spacing, thus improving the sensitivity of thedevice. The'normal spacing of the coils is not critical, although thespacing has an optimum value which is readily determined by experiment.The coil spacing is adjusted by turning the nuts 3|, the springs 32serving to retain the adjustment. As the microphone may be used invarious positions between vertical and horizontal, the normal coilspacing may vary slightly. However, by making the circuit adjustmentswith the microphone in about a 45 position, changes in the operatingcharacteristics will be minimized. The normal coil spacing is notaffected by the contact between the microphone andvibration-transmitting surface.

As the operation of the microphone depends on the relative position orcoupling of the coils and not on the rate of change of coildisplacement. the microphone is capable of responding to mechanicalvibrations of relatively low frequency.

While the invention is here shown to be embodied in an inertia-typemicrophone, certain features of the invention are also applicable tomicrophones of the diaphragm type.

The modified form of microphone apparatus shown in Fig. 8 is adapted formeasuring or checking the surface finish of a work piece. This apparatusincludes a microphone or translating device I I5 which is generallysimilar to themicrophone I5 of Figs. 1 to 6 and is connected in asuitable electrical system such as that of Fig. 7.

In the modified microphone the coil I6 is sta-- 39 of Fig. 3 is omitted,and is replaced by a pin or stud I38 against which the inner end of thestylus abuts in coaxial relation to the coils, the microphone housingbeing centrally apertured to pass the stud. The stylus is here shown to,extend downwardly from the microphone housing, and passes through acentrally apertured flanged bushing I55 which is rigidly secured to thecrowned end of the housing. The bushing is secured to a carriage I55slidable on a guide member I57 in a direction at right angles to thestylus, the carriage being reciprocated as by means of a link I58. Theplunger is urged downwardly by a light coiled spring I59 surrounding theplunger. A work holder I60, mounted on a support I6I below themicrophone, is adapted to carry a work piece I62. In the case of acylindrical work piece, such as a piston pin, the work holder may be inthe form of a V-block.

In the operation of the device of Fig. 8, the tracing tip I54 of thestylus I53 is brought into contact with the work piece I62, and themicrophone carriage is reciprocated, causing the stylus I53 to slidealong the surface of the work piece. Any surface irregularities on thework piece will produce a vibration of the microphone coil I1,

and will be made evident by one or more of the output devices 22, 23 and24 of the system of Fig. 7. The recorder 22 and voltmeter 24 may becalibrated to indicate the extent of the surface irregularities. Themicrophone is here shown to be movable with respect to the work but itwill be evident that this relation may be reversed.

The modified form of apparatus shown in Figs. 9 and 10 is adapted forgauging or checking dimensions of a work piece. This apparatus includesa translating device 2I5 generally similar to the microphone of Fig. 8,although the device is not used as a microphone but rather as adisplacement indicator. The translating device 2 I5 is secured inhorizontal position to the underside of a bracket 263 mounted on a base264. In this device the coil I1 is the movable coil and is arer isslidably mounted in a shouldered bore 268 formed in a cylindrical bodymember 269, the lower end of which is detachably secured in the ringmember 265 by a set screw 210. The body member has a reduced cylindricalextension 21I at its upper end and is radially slotted to receive abell-crank lever 212 which is pivotally mounted to swing about ahorizontal axis. The lever 212 has a vertical arm which projectsupwardly into the cylindrical extension 2H and is provided with arounded contact portion 213 projecting laterally from the extension, theprojection of the contact portion being limited by an adjusting screw214 engageable with the horizontal arm of the lever and disposed in theupper end of the bore 268. The plunger is urged upwardly by a lightcoiled spring 215 but the adjusting screw 214 prevents the plunger fromlosing contact with the stud 238 on the coil-supporting stem of thetranslating device. The cylindrical extension 21I is adapted toreceive'thereov'er an apertured work piece262 the inner diameter ofwhich is to be gauged by theapparatus, this diameter determining theangular position of the bell-crank lever 212 and thereby determining therelative position of the coils I6 and I1 of the translating device.

The translating device 2I5 is connected in a suitable electrical systemsuch as that shown in Fig. 12. In this system a high-frequencyoscillator 220, similar to the oscillator of Fig. 7, is coupled to theinput circuits of a bridge type vacuum tube voltmeter including a pairof vacuum tubes 216 and 211, preferably of the beam power type. Theinput or grid circuit of the tube 216 includes the variable inductor I6,I1, of the translating device, and in some instances a small adjustableshunting condenser 216, and the input or grid circuit of the tube 211includes a coil. 219 and a small adjustable shunting condenser 288. Theinput circuits of the tubes are coupled to the oscillator by smallcondensers 28 I, and are tuned to a frequency slightly above or belowthe oscillator frequency, as in the system of Fig. 7. The vacuum orthermionic tubes have a common. cathode resistor 282, and the anodes orplates of the tubes are connected to a current source 283 through acenter-tapped resistor 284, the ends of which are connected to theanodes. A directcurrent milliammeter 285, which may be of thezero-center or zero-end type, is connected between the tube anodes andis suitably calibrated. In the case of an instrument movement of thezero-end type, the normal current through the instrument is adjusted tobring the pointer to the,

center of the scale, as by adjusting the condenser 280'or thecenter-tapped resistor 284. same current source is used to supply theoscillator, a tuned choke 286 is connected between the source and theoscillator. The oscillator and associated apparatus, including themilliammeter 285, are housed in a suitable casing 281 mounted on thebase 264.

In the operation of the apparatus of Figs. 9, 10 and 12, the work piece262 is slipped over the vertical extension 21I of the body member,causing the bell-crank lever 212 to turn slightly on its pivotal axisand to depress the plunger 261 which in turn moves the coil I1 closer tothe coil I6, thereby changing the inductance of the connected coils. Thereactance of the input circuit of the vacuum tube 216 is thus changed,causing the plate current of this tubeto change and thereby altering thecurrent flow through the milliammeter 285. The system of Fig. 12 is soadjusted that with a work piece having a bore of normal size the pointerof the milliammeter will be at the zero mark when the work piece is ingauging position. If the bore varies from normal size the meter pointerwill come to rest at a position indicating oversize or undersize, as thecase may be. By turning the work piece on the cylindrical extension 21Iany eccentricities in the bore will cause changes in the pointerposition.

The modified form of apparatus shown in Fig. 11 is adapted for gaugingor checking the external dimension of a work piece, such as acylindrical member 362, and is used in an electrical system such as thatof Fig. 12. The apparatus includes a translating device generallysimilar to the devices of Figs. 8 and 9. The plunger or stylus of Fig. 8is replaced by a plunger 353 which is urged in one direction by a coiledspring 359. The plunger is here shown to merely abut against the studI36, but it will be obvious that the plunger may be rigidly attached tothis stud in which event the spring 359 may be omitted. The mountingbushing I55 is secured to one leg of a U-shaped'frame 388, and the otherleg of the frame is provided with an anvil member 399 in the form of amicrometer head screw-threaded in the frame and aligned with the plunger353.

In the operation of the device of Fig. 11, which is connected in theelectrical system of Fig. 12, the work piece 362 is inserted between theanvil 389 and the plunger 353, causing displacement of the coil I1towards the coil I6. This efiects a deflection of the meter 285, as withthe device of Fig. 9, thereby checking the diameter of the work piece.In some cases the inserted work piece may be turned to check anyeccentricity.

Certain specific embodiments of the invention have been shown anddescribed, but it will be un- If the adapted to transmit mechanicalvibrations to one of said coils, means for resiliently mounting theother coil in said housing, and inertia means for resisting movement ofsaid last-named coil during the vibration of the housing. 2.Electromechanical translating apparatus comprising electromagneticallycoupled coils adapted to be traversed by high-frequency current andrelatively displaceable to vary the coupling thereof, a vibratorysupport for said coils adapted to transmit mechanical vibrations to oneof said coils, means for resiliently mounting another of said coils onsaid support, and inertia means for resisting the movement of saidlastnamed coil during the vibration of the support. 3. Electromechanicaltranslating apparatus comprising electromagnetically coupled coilsadapted to be traversed by high-frequency current and relativelydisplaceable to vary the coupling thereof, a vibratory support for saidcoils adapted to transmit mechanical vibrations to one of said coils,means for resiliently mounting another of said coils on said support,and a damping member secured to said last-named coil and forming adamping chamber with said support.

4. Electromechanical translating apparatus comprisingelectromagnetically coupled coils adapted to be traversed byhigh-frequency current and relatively displaceable to vary the couplingthereof, a vibratory supporting housing for said coils adapted totransmit mechanical vibrations to one of said coils, means forresiliently mounting another of said coils in said housing, and aninertia plate secured to said last-named coil and forming a dampingchamber with said housing.

- 5. Electromechanical translating. apparatus comprisingelectromagnetically coupled coils adapted to be traversed byhigh-frequency current and relatively displaceable to vary the couplingthereof, a vibratory enclosing support for said coils adapted totransmit mechanical vibrations to one of saidcoils, and a pair of spacedspring arms secured to said support for resiliently mounting another ofsaid coils. 6. Electromechanical translating apparatus comprising'electro magnetically coupled coils adapted to be traversed byhigh-frequency current and relatively displaceable to vary the couplingthereof, a support for mounting one of said coils, and a pair of spacedspring arms secured to said support and spaced axially of another ofsaid coils for resiliently mounting said lastnamed coil.

7. Electromechanical translating apparatus comprisingelectromagnetically coupled coils adapted to be traversed byhigh-frequency current and relatively displaceable to vary the couplingthereof, a support, a pair of spaced spring arms secured to saidsupport, said coils being disposed between said spring arms, means formounting one of said coils on said support, and means including a memberconnecting the defiectable portions of said spring arms for mountinganother of said coils.

8. Electromechanical translating apparatus comprisingelectromagnetically coupled coils adapted to be traversed byhigh-frequency current and relatively displaceable to vary the couplingthereof, a support having parallel studs, a carrier member for one ofsaid coils slidable on said studs, coiled springs on said studs forurging said carrier member in one direction, screwthreaded membersengaging said studs and forrning adjustable stops for the carrier memberto vary the position of the associated coil, and resilient means forsupporting the other coil.

ROYAL LEE.

REFERENCES CITED The following references are of record in the file ofthis patent: I

UNITED STATES PATENTS Number Name Date 281,240 Cheever July 17, 1883314,155 Taylor Mar. 1'7, 1885 1,680,399 Thomas Aug. 14, 1928 2,005,887Carson June 25, 1935 2,043,180 La Fave June 2, 1936 2,081,738 ConoverMay 25, 1937 2,083,759 Temple June 15, 1937 2,209,213 Vernon July 23,1940 2,235,533 Roberts Mar. 18, 1941 2,261,541 De Sart Nov. 4, 19412,288,838 Pike et a1. July 7,1942 2,305,626 Lee Dec. 22, 1942 2,357,745Kliever Sept. 5, 1944 2,364,237 Neif a Dec, 5, 1944 2,392,758. MintonJan. 8, 1946 FOREIGN PATENTS Number Country Date 326,296 Great BritainMar. 13, 1930 Patent No. 2,479,072

Certificate of Correction August 16, 1949 ROYAL LEE It is herebycertified that errors appear in the printed specification of the abovenumbered patent requiring correction as follows:

Column 2, line 26, for the numeral 500 read 5000; column 3, line 40, forthe words forms on read forms an;

and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in thePatent Office.

' s Signed and sealed this 3rd day of January, A. D. 1950.

THOMAS F. MURPHY, Assistant Gammz'ssioner of Patents.

